Method and apparatus for polygonal heat slug

ABSTRACT

An electronic package which has a polygonal shaped heat slug. The heat slug extends from a top surface of a package which has a plurality of vias. The package also has a number of capacitors that are mounted to the top surface. Some of the capacitors are located between the heat slug and the vias. The polygonal shape of the heat slug provides additional space on the top surface so that capacitors can be added without eliminating vias from the package.

CROSS REFERENCE TO RELATED APPLICATION

This application claims the benefit of and is a continuation of U.S.Application Ser. No. 08/626,174, filed Mar. 29, 1996 now U.S. Pat. No.6,256,189, entitled ‘HEAT SLUG DESIGN WHICH FACILITATES MOUNTING OFDISCRETE COMPONENTS ON A PACKAGE WITHOUT LOSING LANDS OR PINS IN THEPACKAGE’, now issued.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a package for an integrated circuit.

2. Description of Related Art

Integrated circuits are typically housed within a package that issoldered to a printed circuit board. Some packages contain a heat slugto facilitate the removal of heat generated by the integrated circuit.The package may also contain a number of discrete capacitors whichfilter the power and/or signals provided to the integrated circuit.

FIG. 1 shows a top surface of an integrated circuit package 2 of theprior art. The package 2 has a rectangular heat slug 4 that issurrounded by a number of through hole vias 6. The vias 6 provideinterconnect to a plurality of lands located on the opposite bottomsurface of the package. The lands are typically soldered to an externalprinted circuit board. The number of lands for the package are typicallylimited by the number of vias 6 that can be formed in the package 2.

Mounted to the top surface of the package are a number of capacitors 8.The capacitors 8 are mounted to surface pads 10 located on the topsurface. The capacitors 8 and accompanying pads are relatively large andoccupy valuable space on the top of the package. Some of the vias 6 mustbe eliminated to provide room for the capacitors. Eliminating viasreduces the number of lands and the pin throughput of the package.Adding more capacitors to the package would necessitate the eliminationof more vias and further reduce the output pins of the package. It wouldbe desirable to provide a package design that can add capacitors withouteliminating more vias and corresponding lands.

SUMMARY OF THE INVENTION

The present invention is an electronic package which has a polygonalshaped heat slug. The heat slug extends from a top surface of a packagewhich has a plurality of vias. The package also has a number ofcapacitors that are mounted to the top surface. Some of the capacitorsare located between the heat slug and the vias. The polygonal shape ofthe heat slug provides additional space on the top surface so thatcapacitors can be added without eliminating vias from the package.

BRIEF DESCRIPTION OF THE DRAWINGS

The objects and advantages of the present invention will become morereadily apparent to those ordinarily skilled in the art after reviewingthe following detailed description and accompanying drawings, wherein:

FIG. 1 is a top view of an electronic package of the prior art;

FIG. 2 is a top view of an electronic package of the present invention;

FIG. 3 is a bottom view of the package shown in FIG. 2;

FIG. 4 is a cross-sectional view of the package shown in FIG. 2.

DETAILED DESCRIPTION OF THE INVENTION

Referring to the drawings more particularly by reference numbers, FIGS.2-4 show an electronic package 20 of the present invention. As shown inFIG. 2, the package 20 has a heat slug 22 extending from the top surface24 of a substrate 26. The heat slug 22 has a polygonal shape to reducethe overall area of the slug 22. In the preferred embodiment the heatslug 22 has an octagonal shape. Although an octagonal shape is shown anddescribed, it is to be understood that the heat slug 22 may have anyshape that has at least five sides. The heat slug 22 is preferablyconstructed from a thermally conductive material such as a nickel platedcopper.

The substrate 26 is preferably a printed circuit board which has atwo-dimensional array of vias 28. The vias 28 on the top surface of thepackage 20 typically extend to via pads 30 located on the bottom surface31 of the package shown in FIG. 3. The via pads 30 are connected tocorresponding land pads 32. The land pads 32 are typically soldered toan external printed circuit board (not shown). Although land pads 32 ina land grid array (LGA) package are shown and described, it is to beunderstood that the package may contain pins within a pin grid arraypackage (PGA), or solder bumps within a ball grid array (BGA) package.Additionally, although a printed circuit board is shown and described,it is to be understood that the substrate 26 may be constructed fromother materials such as co-fired ceramic.

Referring to FIG. 2, the package 20 has a plurality of discreteelectronic devices 34 mounted to the top surface of the substrate 26. Inthe preferred embodiment, the discrete devices 34 are capacitors. Thecapacitors 34 typically filter power and/or signals provided to thepackage. Although capacitors are shown and described, it is to beunderstood that the discrete devices 34 may be any active or passivecomponent such as a resistor.

The devices 34 are preferably soldered to a pair of surface pads 36located on the top surface of the printed circuit board 26. Four of thedevices 34 can be mounted in an area adjacent to a pair of opposingsides 38 and 40 of the heat slug 22. In the embodiment disclosed, theside mounted devices 34 will each eliminate three vias 28 from thepackage to provide room for the surface pads 36.

The package 20 also has four additional devices that are mounted betweenthe corner sides 42-48 of the heat slug 22 and the vias 28. Thepolygonal shape provides enough clearance between the heat slug 22 andthe vias 28 to allow the devices 34 to be mounted to the printed circuitboard 26 without eliminating vias from the package 20. The polygonalshaped heat slug 22 thus provides a package that will support additionalcapacitors without eliminating vias 28 and corresponding land pads 32.

In the preferred embodiment, the heat slug 22 is mounted to a surfacepad 50 of the circuit board 26 which is dedicated to electrical ground(Vss). One surface pad 36 of each device 34 may be routed to the groundpad 50. The other pad 36 may be connected to one of the vias 28 toelectrically couple the devices to the internal circuitry of the package20.

As shown in FIG. 3, the package 20 typically contains an integratedcircuit 52 that is mounted to the package and located within a cavity 54of the printed circuit board 26. The integrated circuit 52 may bemounted directly to the heat slug 22 to improve the thermal performanceof the package. The integrated circuit 52 is coupled to the printedcircuit board 26 by a plurality of bond wires 56. The cavity 54 andintegrated circuit 52 are enclosed by an encapsulant 58. The integratedcircuit 52 is preferably a microprocessor, although it is to beunderstood that the package 20 may contain any electrical device.

The package 20 is typically assembled by initially mounting the heatslug 22 and electrical devices 34 to the printed circuit board 26 with asolder reflow process. The integrated circuit 52 is then mounted to theheat slug 22 and wire bonded to the printed circuit board 26. The cavity54 is then filled with an encapsulant 58 to enclose the integratedcircuit 52.

While certain exemplary embodiments have been described and shown in theaccompanying drawings, it is to be understood that such embodiments aremerely illustrative of and not restrictive on the broad invention, andthat this invention not be limited to the specific constructions andarrangements shown and described, since various other modifications mayoccur to those ordinarily skilled in the art.

What is claimed is:
 1. An electronic package, comprising: a packagewhich has a top surface and an opposite bottom surface; a plurality ofcontacts located on said bottom surface of said package; and, apolygonal shaped heat slug located in said top surface of said package.2. The package as recited in claim 1, further comprising an electricaldevice mounted to said top surface of said package.
 3. The package asrecited in claim 2, wherein said top surface has a two-dimensional arrayof vias and said electrical device is located between said heat slug andsaid vias.
 4. The package as recited in claim 3, wherein said topsurface has a rectangular shape defined by a pair of intersectingdiagonal lines that extend from opposing corners of said top surface,and said electrical device is located on one of the diagonal lines. 5.The package as recited in claim 2, wherein said electrical device is acapacitor.
 6. A polygonal shaped heat slug for an electronic package,comprising: a thermally conductive material having a top surface, abottom surface to couple to a substrate of the electronic package, andat least five sides to reduce the overall area of the heat slug andprovide clearance to mount additional devices to the substrate of theelectronic package.
 7. The polygonal shaped heat slug as recited inclaim 6, wherein at least one of the at least five sides is a cornerside.
 8. The polygonal shaped heat slug as recited in claim 6, whereinthe polygonal shape has eight sides and the polygonal shaped heat slugis octagonally shaped.
 9. The polygonal shaped heat slug as recited inclaim 8, wherein four of the eight sides are corner sides.
 10. Thepolygonal shaped heat slug as recited in claim 6, wherein the substrateof the electronic package is a printed circuit board.
 11. The polygonalshaped heat slug as recited in claim 10, wherein the bottom surface ofthe thermally conductive material couples to a pad of the printedcircuit board.
 12. The polygonal shaped heat slug as recited in claim 6,wherein the thermally conductive material is nickel plated copper. 13.An electronic package, comprising: a printed circuit board having aplurality of contacts on a bottom surface and a plurality of vias on atop surface; an integrated circuit coupled to the printed circuit board;a polygonal shaped heat slug coupled to a surface of the integratedcircuit, the polygonal shaped heat slug having at least five sides toreduce its overall area and provide clearance to mount additionaldevices to the printed circuit board; and, an electrical device coupledto the printed circuit board between the heat slug and at least one ofthe plurality of vias.
 14. The electronic package as recited in claim13, wherein the electrical device is a capacitor.
 15. The electronicpackage as recited in claim 13, wherein the electrical device is coupledbetween a ground pad and one of the plurality of vias.
 16. Theelectronic package as recited in claim 13, wherein at least one of theat least five sides of the polygonal shaped heat slug is a corner side.17. The electronic package as recited in claim 13, wherein the polygonalshaped heat slug polygonal has eight sides and is octagonally shaped.18. The electronic package as recited in claim 17, wherein four of theeight sides of the polygonal shaped heat slug are corner sides.
 19. Amethod of assembling an electronic package, comprising: a) providing aprinted circuit board having a plurality of contacts on a bottom surfaceand a plurality of vias on a top surface; b) mounting an integratedcircuit to the printed circuit board; c) mounting a polygonal shapedheat slug to a surface of the integrated circuit, the polygonal shapedheat slug having at least five sides to reduce its overall area andprovide clearance to mount additional devices to the printed circuitboard; and d) mounting an electrical device to the top surface of theprinted circuit board at a location between the heat slug and one of theplurality of vias.
 20. The method as recited in claim 19, furthercomprising: e) enclosing the integrated circuit with an encapsulant.